Logical operations performed in the optical domain are required to enable ultra-fast all-optical signal processing (AOSP) for next generation all-optical networks. All-optical logic gates can be used to perform many functions for AOSP for packet-switched network applications. These functions include header recognition and/or modification, packet contention, data encoding, realization of half- and full-adders, etc. Semiconductor devices offer the advantage of compact size, low operating power, and relatively high speed.
Up to now, a number of schemes have been proposed to implement different all-optical logical gates exploiting nonlinear effects in optical media. For instance, different logical operators have been implemented in the optical domain exploiting Semiconductor Optical Amplifiers (SOAs). This can be seen in a variety of articles such as “All-Optical Multiple Logic Gates With XOR, NOR, OR, and NAND Functions Using Parallel SOA-MZI Structures: Theory and Experiment” by J. Y Kim et. al., in J. Lightw. Technol., Vol. 24, no 9, September 2006; “An All-Optical XOR Logic Gate for High-Speed RZ-DPSK Signals by FWM in Semiconductor Optical Amplifier” by N. Deng et. al., in J. Sel. Topics. Quant. Electron. Vol. 12, no. 4, July/August 2006; and “All-optical NAND gate using cross-gain modulation in semiconductor optical amplifiers” by S. H. Kim et. al., in Electron. Lett., vol. 41, no. 18, September 2001, all of which are incorporated herein in by reference in their entirety.
Beside SOAs, passive devices are attractive since they are cheaper and do not usually need external circuitry for current sinking and thermal stabilization. Passive saturable absorbers (SAs) comprised of semiconductor multiple Quantum wells (MQWs) have been widely exploited to perform ultra-fast AND operation. This can be seen, for example, in “1 Tbit/s demultiplexing using low temperature grown InGaAs/InAlAs multiple quantum wells” by H. Kobayashi in Electr. Lett. Vol. 34, pp. 908-909, April 1998, which is incorporated herein by reference in its entirety.
Logical operations for AOSP in Microring Resonators (MRs) have been also theoretically and experimentally investigated. This is seen in the articles entitled “40-Gb/s NRZ and RZ Operation of an All-Optical AND Logic Gate Based on a Passive InGaAsP/InP Microring Resonator” by S. Mikroulis in J. Lightw. Technol., vol. 24 no. 3, March 2006; and “All-Optical AND/NAND Logic Gates Using Semiconductor Microresonators by T. A. Ibrahim” et. al. in Photon. Technol. Lett., vol. 15, no 10, October 2003. Both of these references are incorporated herein by reference in their entirety.
Implementation based on SOAs are usually power-consuming and intrinsically noisy, and their cascadability is limited by the amplifier noise figure. Furthermore, in many cases they need careful polarization alignment of the input signals. On the other hand, the nonlinear characteristic of a passive SA, exhibiting low transmittance at low input energy and high transmittance at high input power is suitable to perform only AND operation between incident optical signals. Implementation of microring resonator devices is limited by technological issues that make this solution at the moment still costly and poorly reliable.